This invention relates generally to systems for testing color vision response in living beings, and more particularly, to a system wherein a pair of multicolored light-emitting diodes (LEDs) are used to illuminate respective portions of a bipartite visual field, one such LED being a reference color source, and the other being a comparison color source.
Color vision defects in humans are mostly hereditary and represent functional departures from the performance of the normal trichromatic eye (NTE). The NTE is called "trichromatic" because it requires, in a colorimeter an admixture of three different primary lights, in a well-defined proportion, to achieve arbitrary visible color. Four primary colors are never required in human vision, and therefore no human has a tetrachromatic eye.
If only two primary colors are required to match any arbitary visible light, the eye is considered to be colordefective and is called "dichromatic." In scotopic (night) vision, all human eyes are monochromatic, and under such conditions, lights can be recognized only by their brightness. All lights of equal brightness look alike, and no color vision exists.
Some humans have trichromatic color vision which is only slightly more discriminating than dichromatic vision, or which performs differently than what would be expected of the NTE under the same conditions. Such persons are called "anomalous trichromats" and are considered to be mildly color defective. The more serious deficiencies are red-green dichromacies and are found in approximately 3% of the male human population, and in a negligibly small percentage of the female population. The two kinds of red-green dichromacies, protanopia and deuteranopia, are held to be analogous to two corresponding anomolous trichromacies, protonomaly and deuteranomaly. Taken together, all of the red-green defects are called protan and deutan defects for brevity, and occur in approximately 10% of the male population. The tritan defects, blue-yellow deficiencies, almost never occur congenitally in either sex, but may be found occasionally in eyes which have suffered a retinal injury.
Nearly all color-vision tests concentrate on the more common red-green defects. Protanopia and deuteranopia, the most serious of the color vision defects, can be distinguished by the lower sensitivy of the protanopic eye to red light, as compared against green or yellow light under the same testing conditions. The deuteranopic eye's relative sensitivity to red, as compared to yellow or green light, usually does not differ much from that of the NTE.
The prior art is comprised essentially of two classes of color-vision testing, categorical methods and mensurative methods. Categorical methods are designed to allow the tester to count correct versus incorrect responses; the diagnosis bein made by the number and kind of incorrect responses during the test. In such known tests, booklets of color plates, such as the well known Ishihara or HRR pseudoisochromatic plates are used to display geometrical or other designs which are printed in colors in such a way as to be difficult to see or invisible to color defectives. In such tests, easier plates often are presented first so that recognition of a defect may be made at the point along the booklet at which the first error occurs. A specific diagnosis often may be made by tallying erroneous responses at the end of the test.
A further test in the categorical class, the Farnsworth-Munsell 100-Hue Test allows the testee to arrange colored chips or bits of cloth in order of their color appearance. A diagnosis is made by identifying or counting those which are not ordered correctly. Lanterns of colored light may be used to present stimuli; tbe response of the testee being to categorize the light presented.
Mensurative methods provide a measure of each response of a testee. The diagnosis of a defect is made on the basis of the high variance, or deviant mean value of several such measurements. These tests generally involve a match of two or more lights. Such matches, made by the testee are called isomeric if the spectral composition of the two correctly matched lights is identical. The matches are called metameric if, although correctly matched, they involve light with different spectral composition but the same appearance. A classical example of such a device is the Magel anomaloscope from around the turn of the century. In this well known device, a bipartite matching field is displayed with a spectral yellow light in one half-field and a mixture of spectral red and spectral green in the other. The testee adjusts the intensity of the yellow for various red and green combinations until a metameric match is obtained. A solid state analog of this well known device is described in U.S. Pat. No. 3,947,099.
The system described in the '099 patent suffers from a variety of significant disadvantages. In addition to its complexity, expense, large size, and relatively high weight, the known arrangement requires, in its preferred form, correlated adjustment of the red-green mixture, making difficult the study of a matching as a function of red plus green intensity. Thus, optics are required to create a matching field. The known arrangement further requires at least three separate diode sources for red, green, and yellow light, each such source being vulnerable to calibration drift independently of each other. Only one yellow standard light is provided, thereby requiring prolonged testing to separate protan from deutan defects. Additionally, the known arrangement does not permit isomeric matching of the two half-fields, thereby excluding, or rendering very difficult, a strictly instrumental calibration of the matching point. Finally, the known arrangement utilizes a bipartite field formed of fiber optics which will be grainy in appearance and must have either a thick blocked-off line or an irregular line dividing the two halves of the field. It is well known that the less salient the edge between matching fields, the more accurate the testee's match. Also, with such fiber optics, each broken fiber in the bundle creates a black spot in the field, and large bundles of such optical fibers are difficult and expensive to fabricate with zero breakage.
It is, therefore, an object of this invention to provide a simple and inexpensive system for testing color vision response.
It is another object of this invention to provide a color vision testing system which is highly portable.
It is a further object of this invention to provide a color vision testing system wherein the LEDs whlch provide the multiple color outputs are very stable and have junction temperatures which change substantially simultaneously.
It is also an object of this invention to provide a color vision testing system which does not require optics.
It is an additional object of this invention to provide a color vision testing system which can be calibrated easily using a spectrometer.
It is a still further object of this invention to provide a system for testing color response which can produce a plurality of predetermined reference light colors.
It is still another object of this invention to provide a color vision testing system wherein an isomeric match can be achieved by a testee.